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A typical operon. In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. [1] The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product.
The distance between each gene in the gene cluster can vary. The DNA found between each repeated gene in the gene cluster is non-conserved. [10] Portions of the DNA sequence of a gene is found to be identical in genes contained in a gene cluster. [5] Gene conversion is the only method in which gene clusters may become homogenized. Although the ...
For example, an operon is a stretch of DNA that is transcribed to create a contiguous segment of RNA, but contains more than one cistron / gene. The operon is said to be polycistronic, whereas ordinary genes are said to be monocistronic.
operon A functional unit of gene expression consisting of a cluster of adjacent structural genes which are collectively under the control of a single promoter, along with one or more adjacent regulatory sequences such as operators which affect transcription of the structural genes.
Mechanism of transcriptional attenuation of the trp operon. An example is the trp gene in bacteria. When there is a high level of tryptophan in the region, it is inefficient for the bacterium to synthesize more. When the RNA polymerase binds and transcribes the trp gene, the ribosome will start translating. (This differs from eukaryotic cells ...
Lee et al. (2003) analyzed the trend of gene clustering between different species. They compared Saccharomyces cerevisiae , Homo sapiens , Caenorhabditis elegans , Arabidopsis thaliana and Drosophila melanogaster , and found a degree of clustering, as fraction of genes in loose clusters, of respectively (37%), (50%), (74%), (52%) and (68%).
The trp operon additionally uses attenuation to control expression of the operon, a second negative feedback control mechanism. The trp operon is well-studied and is commonly used as an example of gene regulation in bacteria alongside the lac operon .
Its operon is an example of a prokaryotic silencer. The three functional genes in this operon are lacZ, lacY, and lacA. [6] The repressor gene, lacI, will produce the repressor protein LacI which is under allosteric regulation. These genes are activated by the presence of lactose in the cell which acts as an effector molecule that binds to LacI ...